feat(feedback): in-app user feedback with admin review and account roles

User-facing Feedback screen (Settings -> Info, registered accounts only): a
message (<=1024 runes) plus one optional attachment, an anti-spam gate (one
unreviewed message at a time), and the operator's inline reply with a
Settings/Info badge. Server-rendered admin console section (/_gm/feedback):
unread/read/archived queue with per-user search, detail with read/reply/
archive/delete/delete-all, safe attachment serving (nosniff, images inline via
<img>, others download-only). Introduces account_roles, the first per-account
role table; feedback_banned blocks only feedback submission, granted/revoked
from /users and the delete-with-block action.

- migration 00004_feedback (feedback_messages + account_roles) + jetgen
- backend internal/feedback (store+service), internal/account/roles.go
- wire: FlatBuffers feedback.submit/get/unread; gateway guest gate (Op.NonGuest,
  is_guest via session resolve) -> guest_forbidden before any backend call
- reply push reuses NotificationEvent with a new admin_reply sub-kind
- UI: /feedback route + screen, attachment picker, badge, channel detection, i18n
- tests: feedback unit (Go+UI), gateway guest-gate, inttest lifecycle, e2e
- docs: PLAN stage 19, ARCHITECTURE s15, FUNCTIONAL(+ru), TESTING, READMEs

gateway/internal/session/cache.go

@@ -11,10 +11,10 @@ import (
 	"time"
 )
 
-// Resolver resolves a token to an account id at the backend (the cache miss
-// path). backendclient.Client satisfies it.
+// Resolver resolves a token to an account id and its guest flag at the backend
+// (the cache miss path). backendclient.Client satisfies it.
 type Resolver interface {
-	ResolveSession(ctx context.Context, token string) (string, error)
+	ResolveSession(ctx context.Context, token string) (string, bool, error)
 }
 
 // Cache resolves session tokens to account ids, caching hits for ttl.
@@ -30,6 +30,7 @@ type Cache struct {
 
 type entry struct {
 	userID  string
+	isGuest bool
 	expires time.Time
 }
 
@@ -47,19 +48,19 @@ func NewCache(backend Resolver, ttl time.Duration, max int) *Cache {
 	}
 }
 
-// Resolve returns the account id for token, consulting the cache first and the
-// backend on a miss (caching the result). An empty token is rejected by the
-// backend like any unknown token.
-func (c *Cache) Resolve(ctx context.Context, token string) (string, error) {
-	if uid, ok := c.lookup(token); ok {
-		return uid, nil
+// Resolve returns the account id and guest flag for token, consulting the cache
+// first and the backend on a miss (caching the result). An empty token is rejected
+// by the backend like any unknown token.
+func (c *Cache) Resolve(ctx context.Context, token string) (string, bool, error) {
+	if uid, guest, ok := c.lookup(token); ok {
+		return uid, guest, nil
 	}
-	uid, err := c.backend.ResolveSession(ctx, token)
+	uid, guest, err := c.backend.ResolveSession(ctx, token)
 	if err != nil {
-		return "", err
+		return "", false, err
 	}
-	c.store(token, uid)
-	return uid, nil
+	c.store(token, uid, guest)
+	return uid, guest, nil
 }
 
 // Invalidate drops a token from the cache (e.g. after a revoke).
@@ -69,25 +70,26 @@ func (c *Cache) Invalidate(token string) {
 	delete(c.entries, token)
 }
 
-// lookup returns a live cached account id for token.
-func (c *Cache) lookup(token string) (string, bool) {
+// lookup returns a live cached account id and guest flag for token.
+func (c *Cache) lookup(token string) (string, bool, bool) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	e, ok := c.entries[token]
 	if !ok || !c.now().Before(e.expires) {
-		return "", false
+		return "", false, false
 	}
-	return e.userID, true
+	return e.userID, e.isGuest, true
 }
 
-// store caches token -> userID, sweeping expired entries and bounding the size.
-func (c *Cache) store(token, userID string) {
+// store caches token -> (userID, isGuest), sweeping expired entries and bounding
+// the size.
+func (c *Cache) store(token, userID string, isGuest bool) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	if len(c.entries) >= c.max {
 		c.evictLocked()
 	}
-	c.entries[token] = entry{userID: userID, expires: c.now().Add(c.ttl)}
+	c.entries[token] = entry{userID: userID, isGuest: isGuest, expires: c.now().Add(c.ttl)}
 }
 
 // evictLocked removes expired entries and, if still at capacity, drops arbitrary